The present embodiments relate to a method for operating a particle therapy system and the particle therapy system.
Particle therapy systems are used for treating tumors using heavy particles such as, for example, protons or carbon ions. This includes irradiating a tumor with heavy particles using a raster scan method, for example. As well as tumors of patients, phantoms may also be irradiated (e.g., for research or maintenance purposes). The basis of the raster scan method is that the intensity of the radiation delivered by a particle generation and acceleration device is set for each ISO energy layer, and the dose applied to each raster scanning point is acquired in realtime and maintained for each scanning point until the planned target dose is reached. The radiation may be switched on and off with the aid of fast magnets, for example. Since a minimum time per scanning point is used while the radiation is applied to a scanning point, the minimum time, during which the radiation is applied to a scanning point at a minimum dose, determines the maximum beam intensity that may be used. The technological schemes for extracting the particle beam from the particle generator and accelerator device may lead to particle stream profiles that are subject to great fluctuations. Typical schemes for extracting the particle beams are, for example, resonance extraction or extraction using a knock-out exciter (e.g., KO exciter). The generated particle stream profiles are dominated by rapid fluctuations in the range of several microseconds and change (e.g., at the start of the extraction in addition to a time domain of several tens of milliseconds up to several seconds).
FIG. 2 shows a variation in intensity over time of a particle beam according to the prior art. The intensity was measured at a resolution of 50 μs. Both the long-term fluctuations and the very short-lived fluctuations are shown.
A method for emitting radiation of a charged particle beam and an acceleration device are known from JP-11329800. The acceleration device includes a device for impressing a high frequency, a deflecting device for an emission, a current measuring device and a calculating machine. The device for impressing the high frequency generates a high-frequency electric field, magnetic field or electromagnetic field on the basis of a high-frequency signal in order to impress the high-frequency field onto a charged particle stream. The deflecting device emits the charged particle beam that is moved outside of a resonance stability limit by the device for impressing the high frequency. The current measuring device measures a value of a current of the charged particle beam that is emitted by the deflecting device for an emission. The calculating machine determines an intensity of the high-frequency signal in accordance with the value of the current measured by the current measuring device.
Due to the strong fluctuations in particle beam intensity, which is evident in, for example, resonance extraction, radiation technology is currently implemented such that irradiation intensities exhibiting very high variability are accepted. Relatively long radiation exposure times are accepted that are dominated by the dose of scanning points having the lowest dose. In order to obtain acceptable radiation exposure times, the minimum doses per scanning point are set to a relatively high level at the planning stage. In this way, extreme cases, in which the duration of the beam application becomes very long due to the restriction to the small intensity, may be avoided. In certain situations, disproportionately high doses may be accepted at scanning points with a low dose requirement.